The invention relates to a clutch system for closing and interrupting a force flow, having a clutch actuator to which a pressure medium can be applied, a first electrically actuatable valve device, and a second electrically actuatable valve device. Pressure medium can be supplied via the first valve device to a switching chamber of the clutch actuator to build up pressure and supplied pressure medium can be discharged again via the second valve device to release pressure. The clutch system interrupts or closes the force flow at a pressure P≧Pd in the switching chamber.
Furthermore, the invention relates to a method for operating a clutch system for closing and interrupting a force flow, having a clutch actuator to which pressure medium can be applied, a first electrically actuatable valve device, and a second electrically actuatable valve device. Pressure medium is supplied via the first valve device to a switching chamber of the clutch actuator to build up pressure and supplied pressure medium is discharged again via the second valve device to release pressure. The clutch system interrupts the force flow at a pressure P≧Pd in the switching chamber.
Such a clutch system is known, for example, from DE 10 2006 035 134 A1 and is shown in schematic form in FIG. 2.
FIG. 2 shows a clutch system 10 having a clutch actuator 12 including a switching chamber 18, a first valve device 14 and a second valve device 16, which are coupled to a supply connection 36 or a deaeration connection 54, respectively. The first valve device 14 includes a first aeration valve 38′ and a second aeration valve 40′, which are arranged in parallel to one another in series with a throttle 46 or a throttle 48, respectively. The first aeration valve 38′ and the second aeration valve 40′ are implemented as electrically activatable 2/2-way valves, which are transferred in the deenergized state by a restoring spring 42′ or a restoring spring 44′, respectively, into their closed switching positions. The provision of aeration valves 38′, 40′ arranged parallel to one another represents a redundant design of the first valve device 14. The number of the aeration valves 38′, 40′ arranged parallel to one another is thus arbitrarily variable.
A filter 32 and a check valve 34 are arranged between the first valve device 14 and the aeration connection 36. The second valve device 16 includes a first deaeration valve 24 and a second deaeration valve 26′, which are arranged parallel to one another and in series to a throttle 20′ or 50′, respectively. The first deaeration valve 24 and the second deaeration valve 26′ are implemented as electrically activatable 2/2-way valves, which are transferred in their deenergized state by a restoring spring 22 or a restoring spring 52, respectively, into their closed switching positions. Since the parallel arrangement of both deaeration valves 24, 26′ in the second valve device 16 is also a result of redundancy, their number, analogously to the number of the aeration valves 38′, 40′ arranged parallel to one another in the first valve device 14, is also variable.
Pressure medium, for example, compressed air or hydraulic oil, is supplied to the illustrated clutch system 10 via the supply connection 36. Backflow of the supplied pressure medium is prevented by the check valve 34. The supplied pressure medium is purified by the filter 32, in order to prevent contamination-related failures of the downstream components, in particular the first valve device 14 and the second valve device 16. By energizing one or both aeration valves 38′, 40′ in the first valve device 14, the pressure medium can reach the switching chamber 18 of the clutch actuator 12 and cause a buildup of pressure therein. If the pressure P prevailing in the switching chamber 18 exceeds a switching pressure Pd required for actuating the clutch system 10, the clutch actuator 12 is actuated to interrupt or close a force flow. For example, the clutch provided in a drivetrain of a motor vehicle can be opened or closed, respectively, so that a force transmission from the drive motor of the motor vehicle to the wheels of the motor vehicle is produced or interrupted, respectively. By energizing the first deaeration valve 24 and/or the second deaeration valve 26′, which are arranged in the second valve arrangement 16, the pressure P prevailing in the switching chamber 18 can take place by discharging the pressure medium present therein via the deaeration connection 54.
The actuation of the illustrated clutch system 10 is typically made possible by a control unit (not shown), which can activate either the first valve device 14 or the second valve device 16 to actuate the clutch actuator 12. The illustrated clutch system 10 is designed so that in the event of a power failure, the pressure P prevailing in the switching chamber 18 is maintained, since both the first valve device 14 and also the second valve device 16 are transferred into blocking switching states by the restoring springs 22, 42′, 44′, 52.
This behavior of the clutch system 10 is problematic, however, if in the event of a deaerated switching chamber 18, a leak of the aeration valves 38′, 40′ in case of defect results in an uncontrolled pressure increase in the switching chamber 18, which could result in an undesired actuation of the clutch actuator 12 and/or a pressure-related overload of parts of the clutch.
The present invention is based on the object of solving these problems.
This and other objects are achieved according to the invention in that measures are provided in order, in the event of a defect of the first valve device and the second valve device, to avoid a subsequent pressure increase in the switching chamber which is sufficient to actuate the clutch system. Undesired actuation and a pressure-related overload of the clutch system can be avoided by this measure. Concrete technical implementations are described as examples hereafter.
A safety valve may be provided, which opens at a pressure P≧P1, wherein P1<Pd. Through the provision of the safety valve, a release of pressure in the switching chamber is possible while bypassing the second valve device. The release of pressure can be performed from a settable pressure level P1 of the opening pressure of the pressure-controlled safety valve, wherein the pressure release rate can be selected so that a buildup of pressure is possible beyond the opening pressure P1 of the safety valve through the opening of the first valve device. The pressure buildup rate of the open first valve device is accordingly greater in absolute value than the pressure release rate of the open safety valve, in order to allow normal actuation of the clutch system outside of the case of a defect. In this way, in case of a defect, in particular upon loss of the switching control via the second valve device due to a power failure, a gradual buildup of pressure through small leaks at the aeration valves in the first valve device can be prevented.
It can expediently be provided that the safety valve closes again at a further pressure P≧P2, wherein P1<P2<Pd. If the safety valve used closes again at a pressure level P2>P1, i.e., the safety valve only assumes its open switching state for pressures between P1 and P2, it can be ensured that the clutch system maintains the switching position in case of a defect which it had upon occurrence of the defect, since an actuating pressure P≧Pd already prevailing in the switching chamber is maintained.
It can advantageously be provided that the safety valve is arranged in a housing wall of the switching chamber. The arrangement of the safety valve in the housing wall of the switching chamber allows a simple and space-saving installation of the safety valve, wherein, in particular, no complete redesigns of previously used valve devices are required to integrate the functionality according to the invention.
Furthermore, a throttle may be provided, which is arranged in the second valve device and whose cross section is designed so that in the case of comparable switching states, a release of pressure occurring per unit of time via the second valve device is greater than a buildup of pressure occurring per unit of time via the first valve device. In particular, all switching states in which the same number of deaeration valves and aeration valves are simultaneously closed or open, respectively, are considered to be comparable switching states. In this way, an uncontrollable pressure increase in the switching chamber can be reliably prevented, as long as the valve provided in series to the throttle in the second valve device can be transferred into its open switching position. In particular, in this way an emergency operation of the clutch system can be ensured, if switching of the first valve device is not possible and it remains in its open switching position, for example, due to jamming or due to a mechanical defect. Furthermore, a leakage flow of the first valve device, i.e., the pressure medium flow, which flows through the first valve device in spite of the closed switching position, is simultaneously less than a further leakage flow of the second valve device.
In particular, a restoring spring may be provided, which is arranged in the first valve device and is designed so that a leakage flow of the first valve device is less than a further leakage flow of the second valve device. For example, the leakage flow of the first valve device can be reduced by the use of a harder restoring spring, which exerts a higher spring force on a switching piston of the aeration valve used. In the case of valves which are identical, except for the restoring springs used, in the first valve device and in the second valve device, accordingly, through the provision of a harder restoring spring in the first valve device than the restoring springs used in the second valve device, the leakage flow of the first valve device can be reduced to a value which is less than the leakage flow of the second valve device. This prevents a gradual buildup of pressure in the switching chamber, since the leakage flow flowing in via the first valve device can also flow out completely as the leakage flow of the second valve device when the second valve device is closed. In the event of a loss of the switching control via the valve devices, the switching chamber is therefore reliably prevented from “filling up”.
An electrically switchable deaeration valve can expediently also be provided, which is arranged in the second valve device and is open in the deenergized state. In this way, in case of a defect, i.e., in particular in the event of a power failure, in which the first valve device and the second valve device are no longer switchable and are transferred into their mechanically predefined idle switching positions, a gradual buildup of pressure in the switching chamber by a leak in the first valve device, which is actually to assume its closed switching position, can be prevented.
In the method according to the invention, in the event of a defect of the first valve device and the second valve device, a subsequent buildup of pressure in the switching chamber sufficient for actuating the clutch system is avoided. In this way, the advantages and special features of the clutch system according to the invention are also implemented in the scope of a method. This also applies for the following particularly preferred embodiments of the method according to the invention.
This method is refined in that a safety valve is opened at a pressure P≧P1, wherein P1<Pd.
It can expediently be provided that the safety valve is closed again at a pressure P≧P2, wherein P1<P2<Pd.
It can advantageously be provided that, in the case of comparable switching states, more pressure medium is discharged per unit of time via the second valve device than is supplied per unit of time via the first valve device.
Furthermore, it can be provided that a leakage flow is caused by the first valve device which is at least compensated for by a further leakage flow caused by the second valve device.
It can expediently be provided that the second valve device is an electrically switchable valve, which is switched into its open switching position in the deenergized state.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.